#ifndef CAFFE_EXP_LAYER_HPP_
#define CAFFE_EXP_LAYER_HPP_

#include <vector>
#include "caffe/blob.hpp"
#include "caffe/layer.hpp"
#include "caffe/proto/caffe.pb.h"
#include "caffe/layers/neuron_layer.hpp"


namespace caffe {

/* @brief Computes @f$ y = \gamma ^ {\alpha x + \beta} @f$,
 *        as specified by the scale @f$ \alpha @f$, shift @f$ \beta @f$, and base @f$ \gamma @f$. */
template <typename Dtype>
class ExpLayer : public NeuronLayer<Dtype> {
 public:
  /* @param param provides ExpParameter exp_param, with ExpLayer options:
   *   - scale (\b optional, default 1) the scale @f$ \alpha @f$
   *   - shift (\b optional, default 0) the shift @f$ \beta @f$
   *   - base (\b optional, default -1 for a value of @f$ e \approx 2.718 @f$) the base @f$ \gamma @f$ */
  explicit ExpLayer(const LayerParameter& param) : NeuronLayer<Dtype>(param) {}
  virtual void LayerSetUp(const vector<Blob<Dtype>*>& bottom, const vector<Blob<Dtype>*>& top);
  virtual inline const char* type() const { return "Exp"; }

 protected:
  /* @param bottom input Blob vector (length 1)
   *   -# @f$ (N \times C \times H \times W) @f$ the inputs @f$ x @f$
   * @param top output Blob vector (length 1)
   *   -# @f$ (N \times C \times H \times W) @f$ the computed outputs @f$ y = \gamma ^ {\alpha x + \beta} @f$ */
  virtual void Forward_cpu(const vector<Blob<Dtype>*>& bottom, const vector<Blob<Dtype>*>& top);

  /* @brief Computes the error gradient w.r.t. the exp inputs.
   * @param top output Blob vector (length 1), providing the error gradient with respect to the outputs
   *   -# @f$ (N \times C \times H \times W) @f$
   *      containing error gradients @f$ \frac{\partial E}{\partial y} @f$ with respect to computed outputs @f$ y @f$
   * @param propagate_down see Layer::Backward.
   * @param bottom input Blob vector (length 1)
   *   -# @f$ (N \times C \times H \times W) @f$
   *      the inputs @f$ x @f$; Backward fills their diff with gradients @f$
   *        \frac{\partial E}{\partial x} = \frac{\partial E}{\partial y} y \alpha \log_e(gamma)
   *      @f$ if propagate_down[0] */
  virtual void Backward_cpu(const vector<Blob<Dtype>*>& top, const vector<bool>& propagate_down, const vector<Blob<Dtype>*>& bottom);

  Dtype inner_scale_, outer_scale_;
};

}  // namespace caffe
#endif  // CAFFE_EXP_LAYER_HPP_
